What is theoretically the heaviest isotope that the R-process could produce?

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AIUI, the R-process in a supernova creates all the heavy isotopes, and that the existence of Pu-244 in the early solar system has been confirmed. It has been stated at the physics stack exchange forum that the theoretically shortest half-life possible is ~ 3 x 10-24 seconds, so let's consider that to be the minimum criteria. I guess this question could be considered inductive starting with "is it possible to create Pu-245 or Am-245", etc., and the work from there. As for the mass of the star, I presume that a most massive star would produce the most massive isotope, and that the most massive star observed is 226 Suns (please correct me if I'm wrong; I found this figure on Wikipedia). Also, let's discount the fact that a neutron star is technically a single nucleus.

Does it turn out that the theoretical heaviest isotope from the R-process of a supernova is basically the same as the most massive isotope that could be artificially produced? I think I've read that the maximum number of protons in a nucleus is 137.
 

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  • #2
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I'm pretty interested in this question too, but you might have an easier time finding an answer in the particle physics forum, maybe?

Also my amateur analysis here is that whatever elements can be produced in a lab, may likely have been produced in a supernova, even more easily. But of course, since they are short lived isotopes, there's no evidence of them in this time. Maybe some clever person in the future might figure out a way to detect the daughter particles, and figure out backwards from there, how much of the original element was there?
 
  • #3
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I'm pretty interested in this question too, but you might have an easier time finding an answer in the particle physics forum, maybe?

Also my amateur analysis here is that whatever elements can be produced in a lab, may likely have been produced in a supernova, even more easily. But of course, since they are short lived isotopes, there's no evidence of them in this time. Maybe some clever person in the future might figure out a way to detect the daughter particles, and figure out backwards from there, how much of the original element was there?
Well, the question pertains to a supernova, so I thought Astrophysics was the proper venue. :)
 
  • #4
Astronuc
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Does it turn out that the theoretical heaviest isotope from the R-process of a supernova is basically the same as the most massive isotope that could be artificially produced? I think I've read that the maximum number of protons in a nucleus is 137.
The heaviest element synthesized on earth is an isotope of Oganesson (Og, Z = 118, A = 294), which has a half-life of 700 microseconds, or 0.7 ms.
https://en.wikipedia.org/wiki/Oganesson
https://en.wikipedia.org/wiki/Isotopes_of_oganesson
https://www.nature.com/articles/d41586-019-00285-9
https://www.rsc.org/periodic-table/element/118/oganesson
https://www.ornl.gov/project/synthesis-new-superheavy-elements-and-nuclei

https://www.nndc.bnl.gov/nudat2/reCenter.jsp?z= 115&n= 173 (select Zoom 1)

https://www.ornl.gov/sites/default/files/Ts_Program Final sm.pdf (Ts, Z = 117)

It's possible that 297Og has been produced, but I've not heard of any verification.

Some are looking beyond 118, to 119, and the next row on the periodic table.
https://www.chemistryworld.com/news...e-next-row-of-the-periodic-table/9400.article

I believe it is speculative to contemplate the heaviest element created in the R-process.
https://en.wikipedia.org/wiki/Supernova_nucleosynthesis#The_r-process
 
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I believe that the idea that the R-process occurs in supernovas was falsified by the "kilonova" collision of two neutron stars. If the R-process is the decay of neutron stars, then your question is meaningless--the heaviest nucleus becomes two neutron stars at the point of collision (several solar masses).
 
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Astronuc
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I believe that the idea that the R-process occurs in supernovas was falsified by the "kilonova" collision of two neutron stars. If the R-process is the decay of neutron stars, then your question is meaningless--the heaviest nucleus becomes two neutron stars at the point of collision (several solar masses).
That also occurred to me, assuming that neutrons are densely packed in a neutron star, then that is effectively are large nucleus, and a collision (or merger) of two neutron stars would be an even larger nucleus.
 
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stefan r
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That also occurred to me, assuming that neutrons are densely packed in a neutron star, then that is effectively are large nucleus, and a collision (or merger) of two neutron stars would be an even larger nucleus.
this depends of definitions. I suggest the neutron star does not count because the binding is gravitational. If a piece of neutron star is measured in a low gravity environment the measurement will show a fragment rather than a large atom. The maximum nucleus needs to be bound by nuclear forces.
 
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stefan r
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As for the mass of the star, I presume that a most massive star would produce the most massive isotope, and that the most massive star observed is 226 Suns (please correct me if I'm wrong; I found this figure on Wikipedia).
I would not assume that. The most massive stars collapse into black holes. We also have pair instability supernovas which create lots of low mass metals.
 
  • #10
ORF
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Hi

Many things in this thread... :)

I will start by direct answer to the OP, and then other side notes

Q: What is the heaviest isotopes synthesized during r-process? There is no experimental data available. According to nucleosynthesis calculations, which take into account very heavy isotopes predict that if you reach very heavy isotopes (because neutron density is high enough) fission plays a key role and one or more fission cycles can take place. Fission of such heavy isotopes is responsible for the observed abundance pattern of elements around mass 140. Rosswog et al have worked a lot in this type of astrophysical environments.

Side notes:
a) According to theoretical models, very heavy isotopes may exist
https://en.wikipedia.org/wiki/Island_of_stability

b) These very heavy nuclei may have an impact in some places:
https://en.wikipedia.org/wiki/Przybylski's_Star#Hypotheses

c) The 137 protons limit is for a stable neutral atom (higher number of protons would make a non-stable neutral atom, but it can still exist)

d) In order to produce very heavy isotopes in a r-process, a huge density of neutrons is required (otherwise neutrons are exhausted before the process reaches such very heavy isotopes). The fraction of heavy elements that is produced by supernovas or compact object collisions is still under discussion (and the contributions of one and the other are not exclusive)

Sorry for long post, I hope it helps

Cheers,
ORF
 
  • #11
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I believe that the idea that the R-process occurs in supernovas was falsified by the "kilonova" collision of two neutron stars. If the R-process is the decay of neutron stars, then your question is meaningless--the heaviest nucleus becomes two neutron stars at the point of collision (several solar masses).
A neutron star is a huge super-nucleus (whether it's held together with gravity is irrelevant). When two of them come together and explode in a kilonova explosion, a lot of neutrons and protons may crack off of it in many different sizes and configurations, including some very large nuclei that we can't necessarily build ourselves in a particle accelerator by smashing alpha particles at larger and larger nuclei. In the neutron star, the nuclei themselves may start out very large, and then decay down to some not quite as large nuclei but still larger than we can produce, that may be stable. That is nuclear isotopes in the island of stability.

If we discover more kilonovas putting spectrometers on them and discerning the spectral lines of elements that we haven't ever seen before might be the way to let us produce them in particle accelerators.
 
  • #12
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this depends of definitions. I suggest the neutron star does not count because the binding is gravitational. If a piece of neutron star is measured in a low gravity environment the measurement will show a fragment rather than a large atom. The maximum nucleus needs to be bound by nuclear forces.
That's why I mentioned the kilonova. The collision and subsequent explosion will form lots of proton and neutron collections that are not gravitationally bound. They will rapidly decay down to (somewhat) stable particles very quickly. Trying to put a limit on the number of nucleons in an unstable nucleus seems futile. So Pb208, the heaviest stable nucleus seems like the right answer. i.e. Wait a few trillion years and it is the heaviest remaining. (Ignoring the issue of possible proton decay.)
 

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